What the Heck Is fibre-based horse feed?

http://www.frankfortonline.com/news/story/560527/with-half-of-britains-horses-overweight-bifid-launches-grainfree-lowsugar-feed-for-the-nations-gooddoers.html

Gentle horse feed for sensitive stomachs, designed to support digestive comfort, hind gut health and easy nutrient absorption. A low sugar fibre-rich formula with naturally sourced ingredients to help maintain steady digestion and overall wellbeing.